1. Field of the Invention
This invention relates to sensor apparatus and, more particularly, to pressure and position sensing apparatus useful in robotics, biometric applications, and the like.
2. Description of the Related Art
Sensors activated by pressure have found a wide variety of applications in every day living, typically, in the form of thin touch pads. Microwave ovens have touch pads for programming cooking times, cellular telephones utilize touch pads as the key pads for dialing phone numbers, elevators have touch pads for calling an up or down elevator and for selecting a floor at which to stop, automated teller machines and computers have utilized touch screens for data entry and selection, intelligent robotic manipulators with pressure sensitive skins, and electronic lock systems such as those used in automobiles and the like use touch pads for keying in the electronic unlocking combination.
In general, these devices are binary devices and only require pressure to be applied at a predetermined position to produce an output. For example, when pressure is applied anywhere on the pad corresponding to the up arrow for an elevator, an up elevator will be called. The same is true for keying in a lock combination. In most cases, each discrete area of the pressure touch pad is individually wired to produce the sensed pressure output for that discrete area. That is, pressing the number “4” on a keypad anywhere on that keypad will produce a signal from the pressed sensor indicating that the number “4” has been pressed.
For the systems described above and other such similar systems, the occurrence of pressure being applied to the sensor is generally the only data that is gathered. The amount of pressure, that is the applied force, is not captured and, for these systems, is usually meaningless. For example, it is only meaningful that a person presses the pad for a down elevator; it is not usually meaningful that the pad is pushed lightly or very hard. Hence, these systems operate in a digital binary mode (e.g., pressure/no pressure) rather than an analog mode (e.g., a continuum of no pressure through heavy pressure).
Position information is not captured by most of these systems. If a person presses an up elevator pad anywhere on the face of the pad, the result is the same and an ascending elevator is called. On a microwave oven, the touch pad is demarcated so that each discrete area corresponds to a particular function (e.g., defrosting or heating popcorn) or a particular number. Pressure on the touch pad between a “1” and a “2” generally produces either one of the two numbers or no response at all and it certainly does not produce an analog result (i.e., a real number) between 1 and 2 based on the point of pressure.
In some applications, a limited amount of predefined position information can be made available. The limited position information is made available by row and column grid arrangements in certain touch screens that indicate the relative position of applied pressure. The position location is relative because it can be accurately located only to the closest grid intersection of a row and a column. In these grid arrangements, it is impossible to measure or resolve the actual position of an applied force when the force is not applied directly over a particular row and column intersection.
Although various devices and systems have been proposed for pressure sensing, none have presented a practical solution that can be employed for simultaneous measurement of the amount of applied pressure and the actual position over a continuous range of positions.